1. A. A. Martinos Center for Biomedical Imaging Massachusetts General Hospital Harvard Medical School 149 13th Street, Suite 2301 Charlestown MA 02129 USA
2. Department of Biological Engineering and Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge MA 02139 USA
3. Department of Chemistry and Biochemistry The University of Arizona 1306 E. University Boulevard Tucson AZ 85721-0041 USA
4. Chemical Sciences and Engineering Division Argonne National Laboratory Argonne IL 60439 USA